Reversible fluorous phase-switching of pyridyl-tagged porphyrins: Application to the sensing of histamine in water

Upon stirring a chloroform/perfluorodecalin biphasic system, the 5,10,15,20-tetrapyridyl porphyrin (TPyP) solubilized in the organic phase was almost quantitatively extracted (∼99.9%) into the fluorous phase containing an excess of the “heavy fluorous” copper(II)-carboxylate complex 1. The porphyrin was quantitatively and almost instantaneously released into the chloroform after addition of excess tetrahydrofuran (THF), which successfully competed with the pyridine ligand for binding sites on complex 1. Metallation of TPyP by copper(II) ions was never observed during the “catch-and-release” process. With the 5,10,15-tripyridyl-20-phenylporphyrin (TPyMPP) or the 5,15-dipyridyl-10,20-diphenylporphyrin (trans-DPyDPP) both efficient extraction (98%) and metallation occurred simultaneously leading to the immobilization of the metallated copper(II)-porphyrins in the fluorous phase. The metalloporphyrins were quantitatively released in the organic phase by addition of THF. With the 5-pyridyl-10,15,20-triphenylporphyrin (MPyTPP) no extraction but rapid metallation was observed under biphasic stirring leading to the quantitative recovery of the Cu²⁺-metalloporphyrin in the organic phase. The “catch-and-release” methodology of TpyP was exploited to develop a triphasic C₆F₁₄/DCM/water indicator displacement assay (IDA) for histamine in which the receptor–indicator complex is compartimentalized in the perfluorocarbon. It has been shown that in such IDA methodology the fluorous phase can play the role of a membrane impervious to water, allowing the detection of histamine in water at micromolar concentrations.